This study characterized FapA as an intrinsically disordered chaperone that inhibits nucleation of the Pseudomonas functional amyloid FapC and reshapes the resulting fibrils. Using CD, SAXS, NMR, ThT, TEM, SEC and Flow Induced Dispersion Analysis (FIDA), the authors mapped how FapA engages the FapC system. On a Fida 1 instrument, FIDA measured the hydrodynamic radius of FapA (~25 Å, consistent with a disordered protein) and gave in-solution evidence that FapA forms a complex with FapC but not its homolog FapB, the size increase indicating a relatively weak interaction. It is an example of using FIDA to measure protein size and complex formation in solution.